The communications industry is rapidly changing to adjust to emerging technologies and ever increasing customer demand. This customer demand for new applications and increased performance of existing applications is driving communications network and system providers to employ networks and systems having greater speed and capacity (e.g., greater bandwidth). In trying to achieve these goals, a common approach taken by many communications providers is to use packet switching technology, particularly ATM switching technology.
Consumers and designers of these systems typically desire high reliability and increased performance at a reasonable price. A common technique for helping to achieve these goals is for these systems to provide multiple paths between a source and a destination. It is typically more cost-effective to provide multiple slower rate links or switching paths, than to provide a single higher rate path. Packets belonging to a packet stream are then distributed (e.g., multiplexed) among multiple paths at a source point. These distributed packets are transported across multiple links and then typically merged back into a single stream of packets at a destination point.
One such mechanism for merging these packets into a packet stream is described in “Inverse Multiplexing for ATM (IMA) Specification Version 1.1,” Document No. AF-PHY-0086.001 (Final Ballot—Draft #1), December 1998, hereafter referred to as the “IMA Specification.” An example of such a technique extracted from the IMA Specification is illustrated in FIG. 1A, in which a stream of ATM cells is input into an IMA group device, distributed across three physical links, and merged back into a the original stream of ATM cells.
As with most communications devices, there is always a potential for an error on a link or within some other component of the communications system. Once such transient error condition that may occur is an out of IMA frame (“OIF”) anomaly. The IMA Specification provides a state diagram for when a particular link should transition between an IMA working state, an OIF anomaly, or a loss of IMA frame (LIF) defect state. This state diagram reproduced herein in FIG. 1B. The IMA Specification further provides that: (a) on a given link, the IMA receiver shall pass to the ATM layer from the IMA sub-layer any cells accumulated before the occurrence of an OIF anomaly on that link (R-117); (b) the IMA receiver shall pass from the IMA sub-layer to the ATM layer no cells received on a link during an OIF anomaly condition reported on that link (R-118); and (c) the IMA receiver shall replace with Filler cells all ATM layer cells received on a link after an OIF anomaly condition has been detected on that link (R-120). Needed are methods and systems for appropriately handling OIF anomalies.